Operating system not found

Hello fellow Microsoft community,i have a Toshiba l355 and recently when i turned on my laptop a screen has popped up saying operating system not found and i would like to know is there anything i can do to fix this,and if so can i kept the stuff or retrieve it. Thanks in advance and sorry if i posted in the work section Sent from my LG-MS840 using WindowsForum mobile app

A few questions if you don't mind answering................ 1. Did you purchase that laptop brand new from reliable outlet, or was that bought 2nd hand? 2. Does this laptop come with Win 8 or with other OS, such as Win 7 or Vista? 3. If the laptop does not come with Win 8, how did Win 8 get installed into the laptop?

I bought the laptop from Walmart in 2010 It originally had vista but i overwrote it with ubuntu then my brother overwrote it with a windows 8 beta that expired a year ago so every hour it cuts off then cuts off after two hours

............my brother overwrote it with a windows 8 beta that expired a year ago..............

Well, what does that tell you ? The operating system has expired. If you want to continue using the computer running with Windows 8, please go buy a full version of Windows 8 with product key and do a clean install.

Not just the product key. You go to, say Walmart, buy a full version of Windows 8 software which will come with a installation DVD and a product key inside a box. Take it home and do a clean install. Here is the tutorial on how to do a clean install :http://www.eightforums.com/tutorials/2299-clean-install-windows-8-a.html Clean install will NOT save anything you already have installed in your computer. If you can still log in to your computer, back up all those you want to save before you do the clean install.

editing................. I mentioned "full version" of Windows 8 because I am not sure if you can revert your computer back to Vista. If you are able to restore your computer back to Vista, then you could do the followings...... 1. Make sure your computer is ready to install Win 8 by running this Win 8 Upgrade Assistant :http://windows.microsoft.com/en-ca/windows-8/upgrade-assistant-download-online-faq 2. Then, you could save a few dollars by buying an "upgrade" version of Win 8.